Wednesday, June 23, 2021

Start With Soil pH

Soil pH in the correct range is needed for maximum yield.

• By Audrey Gamble, Auburn University Extension Soil Scientist •

henry county, alabama zinc deficiency
This Henry County, Alabama, field shows manganese deficiency from a soil pH above 7.0.

Maintaining soil pH is the first step to improving soil fertility for peanut production. Most Southeastern soils are naturally low in pH and must be limed to create conditions that boost production. The ideal pH for peanuts is in the range of 6.0 to 6.5.

Maintaining pH according to soil testing lab recommendations will ensure that the availability of plant nutrients is maximized so any applied fertilizers do not go to waste. Maintenance of soil pH is money well spent for producers because it improves crop quality and yield.

Problems at low pH

When soil pH falls below 6.0, the availability of many macronutrients, such as phosphorus, needed for peanut production decreases. However, the availability of many plant micronutrients, such as zinc, manganese and iron, increases at low pH. Soil pH below the optimum range can increase zinc uptake by peanuts to a toxic level.

dale county, alabama
This Dale County, Alabama, field shows zinc toxicity from a low soil pH.

During the 2019 and 2020 growing seasons, Extension specialists received several calls related to zinc toxicity in peanut. This was likely the result of periods of heavy rainfall during the previous winters. Heavy rainfall can cause leaching of salts from the topsoil, resulting in a “false” high soil pH reading.

Zinc toxicities were confirmed by plant tissue tests where the symptom of split stems was observed. To combat this issue: 1) do not collect soil samples when fields have been saturated for an excess time and 2) lime according to soil tests. If soil pH is

borderline (ex. 5.8 or 5.9), it may be a good idea to go ahead and apply lime.

Problems at high pH

sem splitting
Split stems is a symptom of zinc toxicity.

When soil pH is above 7.0, the availability of many micronutrients, such as manganese, needed for peanut production decreases. It is common to observe manganese deficiency in areas of fields where lime was previously stored.

At a pH above 8.0, peanut yields can be reduced by more than 1 ton per acre from manganese deficiency. High soil pH is not a common problem in the Southeast. To ensure that soil pH does not get too high, apply lime according to soil test recommendations.

In years when soil test calcium is low but pH is in the correct range, apply gypsum at bloom instead of lime as a calcium source.

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